Re: [ATM] Ball bearing for triangles,spherical aberration caused by thermal gradient in the mirror:theresults...(long)

[Raphaël GUINAMARD <rguinamard@infonie.fr>]

Hi Vladimir, thanks for your reply
Yes my scope is a newtonian (dob)
Let me understand you correctly :
You say that if I put many "actuators" screws, to deform slighly the
secondary along an ellipse at let say 2/3 of the circonference, you think
it'll produce astigmatism? Is that what you say?
Do you think a 2/3 value is OK to inverse my undercorrected primary
spherical aberation?
Thanks for your reply
----- Original Message ----- 
From: "vladimir sacek" <v959@msn.com>
To: "atm" <atm@atmlist.net>
Sent: Friday, January 07, 2005 6:21 AM
Subject: Re: [ATM] Ball bearing for triangles,spherical aberration caused by
thermal gradient in the mirror: theresults...(long)


Raphael,

If I understand correctly, you have a 24" f/3.3
Newtonian. If so, the secondary is flat. Banding
a flat would induce much more astigmatism than
spherical aberration; that is definitely not a way
to improve telescope's optics.

You may want to check out the edge quality. TE
can make spherical aberration look worse and, to
unsuspecting eyes, or in compromised conditions,
can even "imitate" s.a.

I will also say that 1/4 wave wavefront level is plenty good
for such a large and fast thin mirror. But I understand
your desire to make it as good as it possibly can be.

Good luck,

Vlad
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